oil pressure drops from 50 to 0 when warm.

B

BlackRat

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Mar 27, 2008
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Ok this if driving me nuts. I have replaced the oil pump. The filter is a new K&N and I am running 10w30 royal purple. I am not running a bypass so everything is forced through the filter. Here is what happens.

-Cold startup I have 50-60 psi.
-190 I have 25 psi.
-After 10 minutes of drive time I have between 0-3 psi.
-I have a mechanical and a electric guage T'ed off of the port above the oil filter. They both read identical.
-The pressure does go up when the motor is revved, but then drops back to zero.
The motor is running good and strong with know noises..... yet......

What is going on!?!?!?!
 
So, after it reaches operating temp, it runs at 25psi and then down to 0-3 while driving for 10 minutes while still at cruise RPM?
 
SmokinBBC said:
So, after it reaches operating temp, it runs at 25psi and then down to 0-3 while driving for 10 minutes while still at cruise RPM?
Click to expand...

No the pressure still raises at cruise speed. When at idle it drops to 0. Someone said that it might be the synthetic oil is to thin for my bearing clearences????
 
I had that problem with a standard oil pump in my 427.
 
Is this a new or seasoned engine? What is the rod side clearance? If it's indeed a lack of volume, get a higher volume pump
 
Twin_Turbo said:
Is this a new or seasoned engine? What is the rod side clearance? If it's indeed a lack of volume, get a higher volume pump
Click to expand...


The motor has less than 500 miles on it. The pump is a hf hp milodon pump that I chage out an L-88 pump for. I don't recall the rod clearence as the paper work got lost in a move. However I have always had good pressure up till now. As I said the only difference that I can think of is the thinner 10\30 RP oil which I did have to ad a couple of qts of 5\30 because it needed it and the store was out of rp 10\30. The oil is very thin but not sure that would have this kind of affect.

Wade
 
I have a melling hv in the BB. I switched from RP10/40 to RP10/30. Pressure at idle dropped from 35 to about 28psi at operating temp.
 
SmokinBBC said:
I have a melling hv in the BB. I switched from RP10/40 to RP10/30. Pressure at idle dropped from 35 to about 28psi at operating temp.
Click to expand...


What oil and viscosity???

Ooops sorry I see now.....
 
Last edited:
Cranked the car and moved it this morning in the garage and it had 60 psi at idle. Of course this was cold. I am hearing no noise from the engine like a bearing knock. I just don't get it!!!!!!!!!
 
BlackRat said:
Twin_Turbo said:
Is this a new or seasoned engine? What is the rod side clearance? If it's indeed a lack of volume, get a higher volume pump
Click to expand...


The motor has less than 500 miles on it. The pump is a hf hp milodon pump that I chage out an L-88 pump for. I don't recall the rod clearence as the paper work got lost in a move. However I have always had good pressure up till now. As I said the only difference that I can think of is the thinner 10\30 RP oil which I did have to ad a couple of qts of 5\30 because it needed it and the store was out of rp 10\30. The oil is very thin but not sure that would have this kind of affect.

Wade
Click to expand...

How much oil did it consume in the first 500 miles?
 
BlackRat said:
The motor has less than 500 miles on it. The pump is a hf hp milodon pump that I chage out an L-88 pump for. I don't recall the rod clearence as the paper work got lost in a move. However I have always had good pressure up till now. As I said the only difference that I can think of is the thinner 1030 RP oil which I did have to ad a couple of qts of 530 because it needed it and the store was out of rp 1030. The oil is very thin but not sure that would have this kind of affect.
Wade
Click to expand...

You say that the engine always had good oil press up til now, but it only had 500 mi on it. Not much history. I suspect that you have a bearing problem.
 
drop the pan and measure rod side clearances, corvettes are easy to drop pans on.
 
I changed the oil back from RP 10w30 to Valvoline VR1 20w50. Oil pressure at cold startup was 70psi. At 190 it was 50 psi at idle. At 210 it was between 25-30 psi at idle. It ran in the driveway for approximately 20 minutes. I have not driven it yet so I don't know that it wont drop to 0 again but from the looks of it it should not. I have no rattling or knocking and I even dropped th clutch at 3 000 and lit the tires up.

Thoughts??????
 
OH hell yeh.....thin oils are worth about 20 psi pressures...in HOT weather...

I use thin oils in northern winters, then went to thick oils in summers....

down here, thin oil is not to be.....and yes there is a difference in fuel economy ...

:hissyfit:
 
I just got back from about a 20 minute cruise. At cruising speed I had 50 PSI continuous @ 2100 rpms and 200 degree temp. Coming to a stop @ idle I had 20-25psi. I did drop to 10-15 psi once but it rebounded. It is pretty cool outside today so I wonder if the oil got warm enough ????? Thoughts????
 
Get an oil temp gauge to check oil temps and see if the pressure reading is in direct relation to the temp. 10psi/1000rpm is enough but it would still worry me that w/ a high volume quality pump you still get that low a pressure. There must be a clearance issue somewhere.
 
would the only fix for a clearence issue be pulling the motor or bearing check and replace while it is in the car??? Or just drive it for now??
 
Depends on where the clearance issues are, if it's rod or main bearings you can do it on the car. if it's the rod side clearance it's either live with it or pull the motor. This was a fresh build right? Were the rods big ends resized? Was the cam ground? What all was done? If the motor was properly blueprinted the bearings should be fine as should the rod side clearance.

maybe it's something stupid, did you check if the oil pump properly seats on the rear cap? is there maybe a little nick or burr on either side? Is the cap lining up nciely with the pump opening or is it partially restricted?
 
This brings back mammories of my '61 Catalina with a full 'race' engine in it....built super loose, enough clearances to rattle ....

I held it together for some 60k miles on the street....at one point I ran two cans of STP goo in there.....

so the inevitable happened of course, got interested in some chick, forgot about the car....and obviously some damn cold front came through...went to zero or below for a week solid....I was walking, the starter could NOT budge that engine.....I even tried lighting a fire under the oil pan...serious....

life was crazy 40+ years ago, and ain't no better NOW, come think of it....

:eek::devil::surrender:
 
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